Sickle cell anemia

1. BIOCHEMISTRY
CASE
PRESENTATION

2. CASE 1
Sickle Cell
Disease
01

3. CASE INTRODUCTION
A 15-year-old African-American female presents to the emergency room with
complaints of bilateral thigh and hip pain. The pain has been present for 1 day
and is steadily increasing in severity. Acetaminophen and ibuprofen have not
relieved her symptoms. She denies any recent trauma or excessive exercise.
She does report feeling fatigued and has been having burning with urination
along with urinating frequently. She reports having similar pain episodes in the
past, sometimes requiring hospitalization.
On examination, she is afebrile (without fever) and in no acute distress. No
one in her family has similar episodes. Her conjunctiva and mucosal
membranes are slightly pale in coloration. She has nonspecific bilateral
anterior thigh pain with no abnormalities appreciated. The remainder of her
examination is completely normal. Her white blood cell count is elevated at
17,000/mm3, and her hemoglobin (Hb) level is decreased at 7.1 g/dL. The
urinalysis demonstrated an abnormal number of numerous bacteria.

4. ◆What is the most likely diagnosis?
◆ What is the molecular genetics behind this
disorder?
◆ What is the pathophysiologic mechanism of
her symptoms?

5. ◆ Most likely diagnosis: Sickle cell disease (pain crisis).
◆ Biochemical mechanism of disease: Single amino acid substitution on hemoglobin
beta chain, inherited in an autosomal recessive fashion (1 of 12 African Americans in
United States are carriers of the trait).
◆ Pathophysiologic mechanism of symptoms: The sickled red blood cells cause
infarction of bone, lung, kidney, and other tissue from vasoocclusion.
CLINICAL CORRELATION
This 15-year-old female’s description of her pain is typical of a sickle cell pain crisis. Many
times, infection is a trigger, most commonly pneumonia or a urinary tract infection.
This case is consistent with a urinary tract infection, indicated by her symptoms of
urinary frequency, and burning with urination (dysuria). Her white blood cell count is
elevated in response to the infection. The low hemoglobin level is consistent with
sickle cell anemia. Since she is homozygous (both genes coding for sickle
hemoglobin), both her parents have sickle cell trait (heterozygous) and thus do not
have symptoms. The diagnosis can be established with hemoglobin electrophoresis.
Treatment includes searching for an underlying cause of crisis (infection, hypoxia,
fever, excessive exercise, and extreme changes in temperature), administration of
oxygen, intravenous fluids for hydration, pain management, and consideration of a
blood transfusion.

6. SICKLE CELL
ANEMIA
02

7. Sickle cell anemia is one of a group of inherited disorders
known as sickle cell disease. It affects the shape of red
blood cells, which carry oxygen to all parts of the body.
Red blood cells are usually round and flexible, so they move
easily through blood vessels. In sickle cell anemia, some red
blood cells are shaped like sickles or crescent moons. These
sickle cells also become rigid and sticky, which can slow or
block blood flow.
There's no cure for most people with sickle cell anemia.
Treatments can relieve pain and help prevent complications
associated with the disease.
Sickle cell disease is more common in certain ethnic groups
including: People of African descent, including African-
Americans(1 in 12 carries a sickle cell gene), Hispanic-
Americans from central and south America, people of Middle
East, Asian, Indian and Mediterranean descent.
What is Sickle Cell Anemia?

8. Normal hemoglobin has four subunits called globins. Adult hemoglobin has two α
(α1 and α2) and two β (β1 and β2) globin chains. Each globin chain has an
associated heme prosthetic group, which is the site of oxygen binding and
release. All globin chains have similar primary sequences.
The secondary structure of globin chains consists of approximately 75 percent α-
helix. The similar primary sequence promotes a similar tertiary structure in all
globins that is called the globin fold, which is compact and globular in overall
conformation.
The quaternary structure of HbA can be described as a dimer of α1β1 and α2α2
dimers. The αβ dimers move relative to one another during the binding and
release of oxygen.

9. Characteristics of Hemoglobin
Hemoglobin must remain soluble at high concentrations within the red blood cell to
support normal oxygen binding and release properties.
This is made possible by a distribution of amino acid side chains in which hydrophobic
residues are sequestered in the interior core of the folded globin subunits, while
hydrophilic residues dominate the water-exposed surface of the globin fold. The
disk-shaped heme prosthetic group is inserted into a hydrophobic pocket formed
by the globin.
Hemoglobin, and the homologous monomeric protein myoglobin (Mb), both bind and
release oxygen as a function of the surrounding concentration, or partial pressure of
oxygen. A plot of percent saturation of Hb or Mb with oxygen versus the partial
pressure of oxygen is called the oxygen dissociation curve. Unlike Mb, which has a
simple hyperbolic oxygen dissociation curve typical of ligand binding to a
monomeric protein, the quaternary structure of HbA allows it to bind oxygen with
positive cooperativity giving a sigmoidal oxygen dissociation curve

10. Protein structure classification
Protein primary (I°) structure: The amino acid sequence of the protein, listed
from the amino-terminal amino acid to the carboxy-terminal amino acid.
Protein secondary (II°) structure: The local three-dimensional spatial
arrangement of amino acids close to one another in the primary sequence.
α-Helices and β-sheets are the predominant secondary structures in
proteins.
Protein tertiary (III°) structure: The overall three-dimensional structure of a
single polypeptide chain, including positions of disulfide bonds.
Noncovalent forces such as hydrogen bonding, electrostatic forces, and
hydrophobic effects are also important.
Protein quaternary (IV°) structure: The overall three-dimensional
arrangement of polypeptide subunits in a multi-subunit protein.

11. What causes Sickle Cell Anemia?
The activity of a given protein is dependent on proper folding of its
polypeptide chain to assume a defined three-dimensional structure.
The importance of protein folding to molecular medicine is emphasized by the
fact that many disease-causing mutations do not directly affect the active
or ligand binding site of proteins, but instead cause local or global
alterations in protein structure or disrupt the folding pathway such that
the native protein fold is not achieved, or undesirable interactions with
other proteins are promoted.
The molecular defect that changes adult hemoglobin (HbA) to sickle
hemoglobin (HbS), leading to sickle cell anemia, is a classic example of
mutations that affect protein structure.

12. What causes Sickle Cell Anemia? Cont’d
Sickle cell Disease which is also known as Sickle Cell Anemia is a single
nucleotide alteration( Point Mutation) in the β globin gene of
Hemoglobin which causes a change of thiamine for adenine (GAG to
GTG) at the six codon of β gene.This change encodes Valine instead of
Glutamic Acid in the six position on the β-globin molecule (Sickle cell
anemia results from the nonconservative substitution of valine for
glutamate at residue 6 (Val-6) in the b-chain of hemoglobin)
The Charge at this site is altered and allows for polymerization of
hemoglobin under conditions of hypoxia. These Properties are
responsible for the profound clinical expression of the Sickling
syndrome.
The Mutant β-globin chain is designated as βs and resulting hemoglobin
referred to as HbS.

13. What causes Sickle Cell Anemia? Cont’d
The intrinsic oxygen binding properties of HbA and HbS are the same,
however, the solubility of deoxy HbS is reduced because of exposure of
Val-6 at the surface of the b-chain.
Since hemoglobin is present at very high concentrations in the red blood cell,
deoxy HbS will precipitate inside the cell. The precipitate takes the form of
elongated fibers because of the association of complementary
hydrophobic surfaces on the β- and α-chains of deoxy HbS.
At oxygen saturations found in arterial blood, the oxy HbS predominates and
HbS does not precipitate because Val-6 of the β-chain is not exposed to
the surface. The tendency for deoxy HbS to precipitate is why clinical
manifestations of sickle cell anemia are brought on by exertion and why
treatment includes administration of oxygen. The stiff fibrous precipitate
causes the red blood cell to deform into the characteristic sickle shape
and makes the normally malleable cell susceptible to hemolysis.

16. Factors Affecting Sickling of RBCs
Extent of Sickling of RBCs depends on the factors that increase the
proportion of HbS in the deoxy state.
These factors include:
• Decreased oxygen tension as a result of high altitude or flying in
non-pressurized plane.
• Increased PCO2
• Decreased PH and
• Increased concentration of 2,3 Bisphosphoglycerate.

17. Consequences of Sickle Cell Anemia
• Reduced life span of RBCs.
• Sickled cells frequently block the flow of blood in the
narrow capillaries . The interruption in the supply of oxygen
leads to tissue anoxia, causing pain and eventually death of
cells( Infarctions) in the vicinity of blockage.
• Because of the disruption of the red cell membrane, the
increased adhesiveness of sickle reticulocyte and the
increased leukocyte count there is a thrombotic
coagulopathy associated with Sickle Cell Anemia that
contributes to the severity of the disease.

18. Signs and Symptoms
Signs and symptoms of sickle cell anemia vary between individuals. Some of
the commonly noted symptoms include:
• Anemia or decreased number of RBCs and oxygen
• Irritability or fussiness in babies
• Severe fatigue or tiredness
• Frequent episodes of pain, also known as crises, in different parts of the
body
• Swelling of hands and feet, associated with pain
• Frequent infections
• Delayed growth noted in children and adults
• Vision problems

19. Complications
If untreated for a prolonged period it may lead to
• Stroke
• Acute chest syndrome, a life threatening complication
• Pulmonary hypertension or high blood pressure in lungs
• Damage to several organs including kidneys, liver, and spleen due to
reduced blood supply
• Blindness
• Sores or ulcers in the legs
• Gallstones
• Priapism or painful, long-lasting erections noted in men with sickle cell
anemia
• Osteoporosis

20. Diagnosis and Treatment
Common tests & procedures
• Prenatal test: Prenatal screening may be performed using amniotic fluid.
• Neonatal screening: Newborn screening is performed by heel prick test.
• Patient history: The doctor talks about family history. Physical exam includes checking for
symptoms like enlargement of spleen and pain.
• Complete blood count (CBC): To check for number of blood cells, particularly RBCs, shape of cells,
hemoglobin type.
• Hb Electrophoresis and High Chromatography(HPLC)
CBC, Hb Electrophoresis and High Chromatography (HPLC) are the gold standard in the diagnosis
of SCD.
Treatment
1.Medications
Analgesics: To reduce pain during crises(Ibuprofen).
Antimetabolite: Reduces episodes of pain; it is also said to stimulate production of normal hemoglobin
(Hydroxyurea).
Amino acid: Reduces acute complications of the disease (L-glutamine).
2.Therapy
Intravenous therapy: Rehydration with intravenous fluids.
Oxygen therapy: Given through a mask to improve breathing.
3.Bone marrow transplantation: Also known as stem cell transplant, the therapy involves introducing
healthy bone marrow stem cells from a donor.

21. SUMMARY

22. 1. Mcgraw Hill Lange Case Files Biochemistry
2. http://medcell.org/tbl/microangiopathy_sickle_cell/reading.php
3. https://www.bing.com/search?q=sign+and+symptoms+of+sickle+cell+anem
ia&form=EDGTCT&qs=UT&cvid=754c8f786d2542bb8adeb1f17d3f2b70&refi
g=efd7eded58d14a2cb62ea89256a47e82&cc=US&setlang=en-
US&plvar=0&PC=HCTS
4. https://www.slideshare.net/namarta28/sickle-cell-anemia-16583474
5. https://www.mayoclinic.org/diseases-conditions/sickle-cell-
anemia/symptoms-causes/syc-20355876#dialogId48872450
References

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